The present invention relates to a lightning conductor with a piezoelectric device for initiating the corona effect.
In per se known manner, a lightning conductor comprises a vertical rod terminated by a metal point or tip and connected to earth by a conductor, which is called a downlead.
The path along which the lightning current flows is constructed in two stages. In a first stage, a downward precursor, constituted by charged particles, which are very often electrons, is directed towards the ground. The general direction of its movement is linked with the local electric field. On the approach of this precursor, objects on the ground undergo an intense electric field and at the most favourable points this leads to the appearance of upward discharges called upward tracers. The first upward tracer which encounters a downward precursor closes the circuit in which the lightning current flows. Thus, the lightning strikes at the point able to emit the fastest upward tracer.
At the approach of the precursors, the lightning conductor tip produces an electric field, which is normally much higher than that in the area surrounding it. It is therefore the most likely point where the upward tracer will start. The efficiency of the lightning conductor, i.e. the extent of the area protected, increases in proportion to the preferred nature of the emission of the upward tracer from the tip compared with the emission of such a tracer from another point.
It is known that the upward precursor is due to the appearance of the corona effect, which consists of an intense electron emission from the tip under the influence of an intense electric field. This electron emission takes place with a time lag of a few dozen microseconds after the electric field has reached the value necessary for initiating the corona effect.
This time lag can be reduced on increasing in the vicinity of the tip, the population of free electrons. The corona effect then starts from a nuclear electron present in the vicinity of the tip, at the instant when the electric field reaches a minimum value below the aforementioned initiating value.
By reducing the time lag of initiating the corona effect on the tip, an upward tracer is consequently produced earlier and will encounter a downward tracer at a higher altitude. This consequently increases the area protected by the lightning conductor.